Electrolytic recording medium



Ov ON Om. Om- ON- K Om Ow l. LIEBLICH Filed March 51, 1964 ELECTROLYTIC RECORDING MEDIUM dum.

'AusNao woudo aanwas-mau asnaalo INVENTOR.

mvlNs LIEBLlcH BY July .25,v 1967 United States Patent O 3,332,857 ELECTROLYTIC RECORDING MEDIUM Irving Lieblich, Elmhurst, N.Y., assignor to Hogan Faximile Corporation, New York, N.Y. Filed Mar. 31, 1964, Ser. No. 356,207 9 Claims. (Cl. 204-2) This invention relates to the art of electrolytic recording, and in particular to an improved electrolytic recording medium or paper. j

Recording paper of the electrolytic type is generally marked by passing the paper between a positive eroding metal anode electrode and a negative non-eroding cathode electrode. The paper is impregnated with an electrolytically conducting solution containing certain ingredients. When a voltage is applied between the electrodes and current is passed through the recording paper, metal ions are introduced into the paper from the anode and reacted with one or more of the ingredients of the paper impregnant to form a colored mark on the recording paper.

In order to be acceptable for facsimile recording purposes, the recording paper preferably should be white initially and should have the ability to produce marks having a density whi-ch is at least close in linear relationship to the current passed through the paper. The density of the marked area should be variable uniformly in a range from White for zero current ow through grays for currents of intermediate magnitude to black for currents of maximum value. The mark preferably should be black so as to provide a good contrast with the white background.

l There should also be a minimum of bleeding or fringing of the mark so as to provide good resolution. The unmarked paper While stored in moist condition in sealed containers 'for extended periods of time prior to use should remain stable without chemical decomposition of its ingredients which would cause discoloration of the paper or affect the reproducibility of results without recorder adjustment. Further, the marked recording paper should not become discolored, give off unpleasant or other odors, or be subject to the transfer of the mark to adjacent materials. The marked recording paper should be insensitive to light even after being repeatedly run through any of the conventional duplicating machines involving exposure to ultraviolet or other strong light sources.

Heretofore successful recording papers have been provided employing pyrocatechin, also called catechol, `as the marking compound. While generally satisfactory some difficulty has been had with the catechol papers because of the tendency of catechol to diffuse or transfer to and to discolor adjacent sheets of paper in contact with or in close proximity thereto. Catechol vapors also may cause discoloration of the walls and other surfaces near the recorder during the recording operation.

Prior to the development of the catechol papers, attempts were made to provide papers utilizing a silver electrode to supply the metal ions which were reacted with a reducing agent to form a mark. Such papers are disclosed in Elsey Patent 2,063,992. Elsey teaches the use of formaldehyde in an aqueous solution of sodium nitrate and sodium hydroxide to form a mark under alkaline conditions by reduction of the silverV ion to metallic silver. However, Elsey states that, although the time factor of reduction to free metal is very small with the solution described, yet during even the time that the 3,332,857 Patented July 25, 1967 ICC silver ion is in solution it may diffuse -away from its point Of origin and so render the lines less sharp and blur the image when reduction finally occurs. Elsey combats lack of sharpness by adding reagents to react even more quickly, not to reduce the silver ion at once but iirst to form insoluble compounds with it. With the silver as insoluble compound once fixed to its point of origin, it is subsequently reduced to free metal. The formulations suggested by Elsey to accomplish his process include polyhydric phenol reducing agents which lare difficult to stabilize in alkaline solutions and so, while purportedly stabilized formulations are disclosed, actually the impregnated papers are unstable and discolor within a few days. Further, the free aldehydes of Elsey, in aqueous solution, have high vapor pressures and thus tend to produce objectional odors. Still further, the inability to maintain a fixed aldehyde concentration presents diiculty in obtaining reproducibility of results.

The present invention aims to provide an improved alkaline electrolytic recording medium which overcomes the foregoing diiculties and disadvantages.

In accordance with the invention an alkaline electrolytic recording medium or paper is provided containing an Ialdehyde addition salt as a reducing agent for metal ions introduced into the paper at the anode side of the paper by the action of electric current. The metal ions are directly reduced to free metal thereby providing a mark. A clear unbl-urred image is obtained with minimal diffusion of the mark. The recording paper is extremely `stable both beforeV and after marking and the recorded mark does not fade even after repeated exposure to light yand heat such as occasioned by being passed through copying machines using strong ultraviolet lamps.

The recording paper in accordance with the invention is advantageous in that there is no perceptible odor therefrom either during or after recording. The impregnant has low vapor pressure thus there is good reproducibility of results. The impregnant is formulated with solid salts easy to handle and very soluble in aqueous solution. The salts are inexpensive and readily obtainable.

Other objects and advantages of the invention will Ibe apparent from the following description of embodiments of the invention.

The aldehyde addition salts in accordance with the invention have the following general formula:

R OH

H/ \SOx n where R=H, alkyl, aryl, or aralkyl,

M=Group IA, zinc, 0r cadmium ion,

n=1 for group IA metal ion or 2 for zinc or cadmium ion, an-d x=2 or 3.

The above stated class may be separated into two groups, first where x=2, and second where x=3. The members of the first group are termed a-hydroxysuliinic acid salts (aldehyde sulfoxylates), and the members of the second group are termed a-hydroxysulfonic acid salts (aldehyde bisuliites).

The simplest a-hydroxysuliinic acid salt is an a-hydroxymet-hanesulinic acid salt, more commonly called a formlaldehyde sulphoxylate, while the simplest a-hydroxysulfonic acid salt is an a-hydroxymethanesulfonic acid salt more commonly called -a formaldehyde bisulfite.

Examples of the aldehyde sulfoxylates are:

Sodium formaldehyde sulfoxylate Potassium formaldehyde sulfoxylate Zinc formaldehyde sulfoxylate Sodium acetaldehyde sulfoxylate Sodium benzaldehyde sulfoxylate Examples of the aldehyde bisultes are:

Sodium formaldehyde bisulte Sodium benzaldehyde bisulte Sodium acetaldehyde bisulte The general concept `of the invention is the use of the aldehyde addition salts as reducing agents for metal ions introduced into the paper by an electric current. A postulated redox reaction for marking with an eroding silver anode when aldehyde sulfoxylates are employed is illustrated below using formaldehyde sulfoxylate anion in an alkaline medium:

A corresponding redox reaction may be given for an aldehyde bisulte as is illustrated by the reaction of formaldehyde bisulte anion in an alkaline medium:

4Ag+ll-CH2 (OH) 80g-+5 OH-e 4Ag-l-CH2O2-l-SOf-f-3H2O Suitable formulations for impregnating into qten square feet of recording paper stock or other porous support are as follows:

Example 1 Grams Sodium formaldehyde sulfoxylate 6 Sodium nitrate 15 Sodium carbonate 1 Sodium bicarbonate 2 Water 100 Example 2 Grams Sodium formaldehyde bisulfite 6 Sodium nitrate 15 Sodium carbonate 1 Sodium bicarbonate 2 Water 100 Example 3 Grams Sodium formaldehyde sulfoxylate 6 Sodium nitrate 15 Sodium hydroxide 0.01

Water 100 Example 4 Grams Sodium formaldehyde sulfoxylate 6 Sodium nitrate 15 Sodium monohydrogen phosphate heptahydrate 7.2

Sodium hydroxide 0.02

Water 100 Example 5 Grams Sodium formaldehyde sulfoxylate 6 Sodium sulfate decahydrate Sodium monohydrogen phosphate heptahydrate 7.2

Sodium hydroxide 0.02

Water 100 Example 6 Grams Sodium acetaldehyde sulfoxylate 6 Sodium nitrate 15 Sodium carbonate 1 Sodium bicarbonate 2 Water 100 Example 7 Grams Zinc formaldehyde bisulte 6 Sodium nitrate 15 Sodium carbonate l Sodium bicarbonate 2 Water Example 8 Grams Sodium benzaldehyde bisulte 6 Sodium nitrate 15 Sodium carbonate 1 Sodium bicarbonate 2 Water 100 With all of the formulations of the examples, satisfactory marks were obtained.

In the ligure there are shown curves illustrating the relationship between diffuse reilectance optical density, as read on a Macbeth diffuse reflectance densitometer, and current ow. This data was obtained by passing recording paper impregnated with the formulation of Example 1 through a conventional facsimile recorder in which a rotating platinum-iridium helical electrode opposed a silver alloy fixed linear electrode. The contact area of the electrodes against the recording medium was about .0001 inch.

Curve 1 was obtained at a spot speed of 23 inches per second. A good black mark of density 1.26 was obtained at thirty-nine volts with a cur-rent ow of milliamperes.

Curve 2 was obtained at a spot speed of 45 inches per second. A good black mark of density 1.20 was obtained at 52 volts with a current ow of 200 milliamperes.

Curve 3 was obtained ata spot speed of 135 inches per second. A good black mark of density 1.02 was obtained at 64 volts with a current flow of 260 milliamperes.

In the examples the concentration of the reducing agent has been set as approximately ve percent by weight, However, it is to be understood that the amount of reducing agent may be varied from `a minimal amount up to the solubility limit thereof.

Further, various combinations of the aldehyde addition salts may be used rather than a single salt. Typical concentrations of reducing agent may vary between 1 and 10 percent by weight. These concentrations are selected as being commensurate with conventional recording speeds and marking apparatus sensitivity. Sensititivity of the imprenated paper increases with increase in concentration of the reducing agent.

It has been `found that the aldehyde sulfoxylates are generally preferred to the aldehyde bisultites for two basic reasons, first, the sulfoxylates have greater stability in alkaline media which may be attributed to a stronger C-S bond in the sulfoxylates, second, the reducing action of the `sulfoxylates is generally stronger than that of the bisullites which is manifest from the difference in oxidation state of the sulfurs in these groups. The sulfoxylates contain sulfur in the di-positive oxidation state whereas in the bisultes the sulfur is in the tetra-positive oxidation state.

Sodium formaldehyde sulfoxylate and zinc formaldehyde sulfoxylate are inexpensive and readily available since they are commonly used in the vat dye industry as dye stripping agents. These compound-s are also used to catalyze the polymerization of vinyl monomers and styrene-butadiene rubber.

Another advantage of the use of the aldehyde sulfoxylates i-s that they may be used at neutral or weakly alkaline pH values. They produce excellent high density black marks at a neutral pH as well as at higher pHs. The use of an acid medium is generally undesirable with the aldehyde sulfoxylates because decomposition of the aldehyde is promoted by acid. However, aldehyde sulfox ylates in weakly acidic recording media will produce acceptable marks if the recording media are used soon after manufacture.

It should be noted that not all reducing agents are satisfactory for the production lof a mark. For example, sodium hydrosuliite, Na2S2O4, is a strong reducing agent but requires a very high pH to produce at best a medium density mark when used as a reducing agent in an alkaline electrolytic recording'paper. In the low to medium alkaline pH ranges where the aldehyde addition salts give good 4density marks the sodium hydrosulite produces a poor low den-sity blue-green mark.

The sodium nitrate is used as an electrolyte. Other suitable electrolytes which might be used are the alkali metal nitrates and sulfatos, and ammonium nitrate or sulfate. The concentration of the salt may be varied as desired -for purposes of varying the electrical conductivity as is known in the art. Such variation may be from minimal amounts to the solubility limits of the respective salts. Combinations of various salts may be made as desired.

It is desirable to provide a pH in the `alkaline range because of the greater stability of these reducing agent-s in a basic medium. The pH may range between 7 and 14. The lpreferred range of pH Vis about 7.0 to 11,0 inasmuch as the paper or other support is generally more resistant to deterioration in this range. Alkali hydroxides, buffers or both may be used to obtain the desired pH value in this range. A carbonate-bicarbonate buffer is preferred because it provides a good medium for the reducing action of the aldehyde addition salts. The advantage of using a buffer is that it will tendy to prevent a ldrift in the pH of the impregnant over a period of time. Suitable alternative buffering agents are monohydrogen phosphate-dihydrogen phosphate and other buffers known in the art.

The eroding anode electrode may be made of silver, silver alloyed with copper and/'or zinc, or any other silver alloy, copper, or any other metal which provides an ion whi-ch may be reduced to give a colored mark It will be noted, for example, that silver produces a good black mark, copper a green mark, and iron a light yellow mark. Silver or silver alloys are preferred anode electrodes because of the high optical den-sity of the mark produced and because of its stable image. Silver, in the production of univalent silver ions, requires less energy than common metal electrodes which produce multivalent ions. The use of silver thus generally results in the production of good density marks with `a small expenditure of power. Silver Ialloy electrodes are available which provide increased hardness, resistance to wear, and resistance to deformation without an appreciable eect upon their marking qualities.

The cathode electrode may be made of any suitable conductive metal able to withstand the abrasive effects of the moving recording paper. Metals found acceptable are platinum, platinum alloys, steel, and others as known in the art.

Recording paper may be prepared by impregnat-ing porous white paper or other porous -support of high wet strength with an impregnant prepared in accordance with the teaching set out herein. The impregnant is permitted to distribute itself evenly throughout the paper. Excess impregnant may be removed by passing the paper between pressure rollers, so that when ready for use in a recorder, the impregnated paper will have about VZ5 to 5() percent moisture by weight. In or-der to retard evaporation, the impregnated paper is stored in suitable sealed containers until needed.

While the invention has been :described and illustrated with reference to specific embodiments thereof, it is to be understood that other embodiments may be resorted to without departing from the invention. Therefore, the form of the invention set out above should be considered as illustrative and not as limiting the scope of the following claims.

Icla-im:

1. An electrolytic recording medium comprising an impregnated sheet containing in .an electrolytically conducting solution an aldehyde addit-ion salt selected from the class consisting of:

R /OH s H SO; n

where R=H, alkyl, aryl, aralkyl,

M=Group IA, zinc, or cadmium ion,

11:1 for group IA metal ion or 2 for zinc or cadmium ion, and

x=2 or 3; the impregnated sheet Iincluding between about 25% and about 50% of moisture by weight of the sheet, and a sealed container disposed around the sheet to keep the moisture content between about 25% and about 50%.

2. A method for forming a mark on an electrolytic recording medium comprising impregnating a porous sheet with a water solution containing an aldehyde addition salt selected from the class consisting of:

R\ /oH H so, n

where:

R=H, alkyl, aryl, aralkyl,

M=Group IA, zinc, or cadmium ion,

r1=1 for group IA metal ion or 2 for zinc or cadmium ion, and

x=2 or 3, the impregnated sheet including between about 25% and about 50% of moisture by weight of the sheet, and a sealed container disposed around the sheet to keep the moisture content between about 25% and about 50%, adjusting and keeping the moisture content of the porous sheet between about 25 to about 50% by weight, moving the sheet between a cathode and a metal anode s-o the sheet is contacted at a localized spot, causing the spot of contact of the cathode land anode to travel in a direction transverse to the direction of movement of the sheet past the cathode and anode, and passing current between the cathode and anode, the anode including a metal which ionizes and en-ters the sheet where it i-s oxidized to form a mark.

3. A method according to claim 2 in which the aldehyde addition salt is selected from the class consisting of sodium formaldehyde sulfoxylate, potassium formaldehyde sulfoxylate, zinc formaldehyde sulfoxylate, sodium acetaldehyde sulfoxylate, sodium benzaldehyde sulfoxylate, sodium formaldehyde bisulte, sodium benzaldehyde bisulte, and sodium acetaldehyde bisulfite.

4. A method according to claim 2 in which the impregnant contains an electrolyte selected from the group corisisting of alkali metal nitrates, alkali metal sulfates, ammonium nitrate and ammonium sulfate.

5. A method according to clairn 2 in which the pH of the impregnant ranges from 7 to 14.

6. A method according to claim 2 in which the impregnant consists essentially in approximate parts by relative weight of reducing agent 6, electrolyte 15, and water 100.

7. A method according to claim 2 in which the 4impregnant is an -aqueous solution containing an electrolyte, and sodium formaldehyde sulfoxylate.

8. A method according to claim 2 in which the impregnant is an aqueous solution containing and electrolyte, and sodium formaldehyde bisulte.

9. A method according to claim 2 in which the impregnant is a solution including in approximate parts by relative Weight water 100, sodium nitrate 15, sodium carbonate 1, sodium bicarbonate 2, and sodium formaldehyde sulfoxylate 6.

References Cited UNITED STATES PATENTS 3,113,910 12/1963 Hepher 204-2 8 OTHER REFERENCES Handbook of Chemistry :and Physics, 37th edition, 1955-1956, Chemical Rubber Publishing C0., page 1622 relied on.

The Condensed Chemical Dictionary, 6th edition, Reinhold Co., pages 591 and 1042 relied on.

JOHN H. MACK, Primary Examiner.

W. VAN SISE, Assistant Examiner. 

2. A METHOD FOR FORMING A MARK ON AN ELECTROLYTIC RECORDING MEDIUM COMPRISING IMPREGNATING A POROUS SHEET WITH A WATER SOLUTION CONTAINING AN ALDEHYDE ADDITION SALT SELECTED FROM THE CLASS CONSISTING OF: 